# san/no-side-effects-in-computed-properties

disallow side effects in computed properties

⚙️ This rule is included in all of "plugin:san/essential", "plugin:san/strongly-recommended" and "plugin:san/recommended".

# 📖 Rule Details

This rule is aimed at preventing the code which makes side effects in computed properties.

It is considered a very bad practice to introduce side effects inside computed properties. It makes the code not predictable and hard to understand.

<script>
/* ✓ GOOD */
export default {
  computed: {
    fullName () {
      const firstName = this.data.get('firstName')
      const lastName = this.data.get('lastName')

      return `${this.firstName} ${this.lastName}`
    },
    reversedArray () {
      return this.data.get('array').slice(0).reverse() // .slice makes a copy of the array, instead of mutating the orginal
    }
  }
}
</script>

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<script>
/* ✗ BAD */
export default {
  computed: {
    fullName () {
      this.data.set('firstName', 'lorem') // <- side effect
      return `${this.data.get('firstName')} ${this.data.get('lastName')}`
    },
    reversedArray () {
      return this.data.get('array').reverse() // <- side effect - orginal array is being mutated
    }
  }
}
</script>

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# 🔧 Options

Nothing.

# 📚 Further Reading

Guide - Computed (opens new window)

# 🔍 Implementation

← san/no-reserved-keys san/no-textarea-mustache →